Anonymous downvoting is the violence of HN (and it's probably a lot more antisocial than we admit). Politely pointing out errors is... well, it's something else. Probably at least OK. Sorry I don't have a Monty Python line for this comment.
More like definitely. What function does downvoting really perform anyway? And what function is it supposed to perform? I see lots of perfectly reasonable comments going grey with no explanation at all.